67 L71, so cal nightmare

[Dave C.]

Re: 67 L71, so cal nightmare

I had to freshen up the motor before I left due to drop in oil pressure, the heads were cracked when someone installed the hardened exhaust seats, pulled it out, ended up replacing the heads , reinstalled and within a week had no oil pressure at idle, pulled it out again and all the mains were into the copper, maybe due to some coolant getting into the oil, I don't know. Anyway had the crank ground, all new bearings, honed the cylinders ( standard bore) new rings, etc . Not sure on all the clearances, but I know they were all checked.

[Carl N.]

Re: 67 L71, so cal nightmare

Sounds like you have already received some great advise. I normally do not respond to these, but I'll toss out couple of ideas. First I assume you replaced timing chain and sprockets when rebuilt, if not this could effect timing. Second, I would assume you "boiled" block and flushed thoroughly before reassembly, sometimes on a 40 + year old block there can have a very solid build up of "crap" in cooling passages. Third, and there was another thread running on this check distributor for shaft run out. Last thought could be proper location of head gaskets - did the assembler check to insure all water passages were open. Sounds like a timing issue to me. I would start with valve lash. And as I continue to ramble on be sure your heater hoses are not reversed nor blocked. Whatever it is, it can be corrected, so don't give up.

[Mark E.]

Re: 67 L71, so cal nightmare

Mark , thanks for your interest in my problem, and my thanks to all the other members that have tried to help me out. I will try to give you some more details, I have set the mechanical advance to 34 * , I have changed out the vac to a b20? ( as per dukes advise, 16* at 12") I have 14" at idle. Idle set at 900. Set the mixture with a vacuum gauge, but I am no expert at this and maybe I have it too lean @ 1 full turn counterclockwise from seated. I have 24* at idle with the vacuum in. At this point if someone knows a great tuneup guy anywhere in the greater LA area, I will load this thing up in my trailer, and haul it there with my motor home, and buy them beer and giv them cash until it is fixed.

By mechanical advance, do you mean centrifugal + initial advance? 34 deg. may be a bit shy but that shouldn't be enough to cause your symptoms.

Can you be specific with the conditions when it overheats, and what the knocking sound is like?

[Dave C.]

Re: 67 L71, so cal nightmare

Carl, all the things you mention were done, other than replacing the timing chain and gears as they were brand new last year.

[Mark E.]

Re: 67 L71, so cal nightmare

If it runs ok long enough for Flight Ops, and you're not planning on PV, maybe go to the meet, enjoy yourself, get ideas, then diagnose it when you get home.

[Dave C.]

Re: 67 L71, so cal nightmare

Mark, the car doesn't really overheat anymore, but something is causing the temperature to rise after a few miles of driving and when that happens it develops a bad spark knock or detonation on any type of acceleration. And yes when I say 34* I mean the initial timing plus the distributor .

[Robert D.]

Re: 67 L71, so cal nightmare

Was the compression ratio calculated after the built. did the builder check the chamber sizes when i did mine my heads my chamber sizes were different so i had to shim the heads alittle bring the compression ratio down. thats where the knocking can be from did you try the increase octane gas yet?

[Michael H.]

Re: 67 L71, so cal nightmare

+1, if over bored much (I set my limits at .03) and not sleeved, overheating is a common issue with all engines.

Michael I agree with you, .030 should be the max for over bore. I bored a 365hp motor years ago to .060 and it ran hot all of the time. If I had to do it over again I would spend the money and re-sleeve any motor requiring any bore over .030. You need that extra metal to help dissipate the heat.

Mike

[Mark E.]

Re: 67 L71, so cal nightmare

Dave says the engine has its standard bore, so hopefully the issue is something minor.

[Dave C.]

Re: 67 L71, so cal nightmare

Was the compression ratio calculated after the built. did the builder check the chamber sizes when i did mine my heads my chamber sizes were different so i had to shim the heads alittle bring the compression ratio down. thats where the knocking can be from did you try the increase octane gas yet?

The compression ratio was checked the first time the motor was put together last year, and it was just shy of a true 11:1. Today's project is to try to find some high octane fuel.

[Duke W.]

Re: 67 L71, so cal nightmare

I recommend limiting CR to about 10.25 on L-71s, especially in CA where the highest commercial octane is 91 PON. I believe Dave can buy 94 at the pump in BC, and cooler pacific northwest temperatures will also help.

Dave is doing the work by himself and he has not been able to determine the centrifugal start and maximum RPM levels and total centrifugal advance because he doesn't have a test tach and has not been able to find a helper to operate the throttle and read the incar tach. Documenting the centrifugal curve is very important and is the next step along with trying some 100LL Avgas or high octane (low vapor pressure) racegas.

As far as ops check is concerned, now that Dave has full time vacuum advance with a B26 (or maybe B20?) both cold start idle speed and fully warmed of idle speed need to be adjusted. The cold idle speed is set with the engine fully warmed up and with Holley's I think you bend a link. The procedure is in the CSM along with the hot fast idle speed. On a cold start initial fast idle will be 2-300 RPM slower than the the hot setting and will slowly increase as the engine warms up or until you kick the throttle.

During ops check the engine is usually only run long enough to get fully warmed up, so overheating shouldn't be an issue, and since you don't take the car out for a drive in Flight Judging detonation won't be an issue.

When dealing with overheating/detonation issues, the first thing to do is fully document the spark advance map. You have to know where you are to figure out how to get where you want to go. Converting to full time vacuum advance with a VAC that meets the Two-Inch Rule is the first thing to do, but Dave has not been able to determine the centrifugal curve start and end points, nor to total centrifugal advance. That's the next step, and once that data is known it's a matter of, first, reducing total WOT advance, but if it has to be reduced to less than 34 degrees, the centrifugal curve should be slowed with stiffer springs.

There are lots of good suggestion in this thread, but 90 percent of the time these problems can be solved or significantly mitigated with adjustments to the spark advance map, so that's what I'm concentrating on in a systematic way. I've done it many times in the past.

I doubt if taking the car to a professional mechanic will do more than throw another monkey wrench into the fan. Most of them don't understand the concept of "spark advance map" or how to adjust it to solve overheating and detonation issues.

I'll be taking all my "tools of the trade" (see the photo in my 2012 San Diego presentation.) to the chapter meet in two weeks, so I can document the spark advance map, or verify what Dave is able to come up with, and we'll go from there.

A question for Dave: What is the initial setting for the idle mixture screws in the CSM and where did they end up after the procedure - number of turns out from the seated position?

Duke

[Michael J.]

Re: 67 L71, so cal nightmare

Oh I forgot to mention, Duke and I had a great conversation the other night , and now he has registered for the Chatworth meet, so he can judge my car personally! This whole thing is very exiting for me. I hope I can get my car running properly soon.

[Duke W.]

Re: 67 L71, so cal nightmare

You probably know, Michael, but you're making me go public with the embarrassment. UCLA didn't make March Madness. In fact they had their worst season since 1948 despite recruiting the best player in the country last year.

Someone hired an airplane that towed a banner over campus on Monday after the PAC-12 tournament (where the Bruins were eliminated in the first round) saying: FIRE THE COACH!

Oregon is the last hope for the PAC-12, and last night's solid defeat of last year's champion Duke was a good omen.

Duke

[Michael J.]

Re: 67 L71, so cal nightmare

You probably know, Michael, but you're making me go public with the embarrassment. UCLA didn't make March Madness. In fact they had their worst season since 1948 despite recruiting the best player in the country last year.

Someone hired an airplane that towed a banner over campus on Monday after the PAC-12 tournament (where the Bruins were eliminated in the first round) saying: FIRE THE COACH!

Oregon is the last hope for the PAC-12, and last night's solid defeat of last year's champion Duke was a good omen.

Duke

[Richard M.]

Re: 67 L71, so cal nightmare

Dave, Sorry about all of the trouble. I've been reading all of your posts. I can relate. Everyone here helped me when I had trouble on the last L71 I worked on.

I just read that you are trying to get a good reading of timing and engine RPM. What type of timing light are you using? I use this one, with a built in tachometer.....
Actron CP7529

http://shop.advanceautoparts.com/p/actron-digital-timing-light-cp7529/9090011-P#

You may be able to get one locally to help your cause and not have to rely on someone reading the dash tach during adjustments.

I wish you all the best to help to solve your problems. Hang in there.

Rich